Within the last nine months, significant progress has been made in the refinement of software and hardware for the imaging of small laboratory animals (rats) at Duke University. At this time (6/12/85), multiple (8 to 16) images can be acquired from an animal during the time required to produce one image. These images, which can be spaced 1.2 to 1.6 mm apart, can be used to closely examine a region of the animal that is 2.0 to 2.5 cm thick. This technique will be used to produce serial images of the brains, livers, and spleens of normal and experimental animals. Preliminary experiments have been conducted using the high field (1.5 Tesla), large-bore (1.0 meter) system. In one experiment, rats that had been fed a hepatocarcinogen for 18 months were imaged. Multiple, discrete hepatic neoplasms ranging from 2 to 12 mm in diameter were readily identified on the images. The images were correlated with gross and histologic sections of the animals. By using a multiple spin echo sequence and by calculating T2 relaxation times, the prolonged relaxation times of the neoplasms were demonstrated. Extracellular space for the neoplasms and for normal liver was calculated using a morphometric analyzer and was compared with the T2 relaxation times for the same lesions. There was a strong, direct relationship between the T2 relaxation time and the percent of extracellular space for the lesions. This may be related to an increase in water content in the neoplasms. Preliminary imaging experiments have also been conducted on rats with mononuclear cell leukemia (enlarge spleen) and on rats to demonstrate normal anatomic structures in the brain. Currently, a study is underway to examine the ability of nuclear magnetic resonance (NMR) imaging to detect pituitary neoplasms in rats.